1. Field of the Invention
The invention relates to a field effect transistor having an electrode coated sequentially by an oxide layer and a nitride layer and a method for manufacturing the same, and more particularly to the field effect transistor and the method for manufacturing this field effect transistor that introduce at least a surrounding-oxide layer and a surrounding-nitride layer to sequentially coat an electrode.
2. Description of the Prior Art
With booming progress in semiconductor technology, various advanced manufacturing processes have been introducing to produce the field effect transistors, especially the metal-oxide-semiconductor field effect transistors (MOSFET).
Referring now to FIG. 1, a schematic cross-sectional view of a typical field effect transistor produced by a conventional manufacturing process in the prior art is shown. This conventional field effect transistor PA1 is structured by forming an electrode PA12 and a gate PA13 inside a trench PA11; in which the electrode PA12 and the gate PA13 are isolated from each other, and the gate PA13 is generally formed as a dimple structure PA131.
Nevertheless, subject to some limitations in the existing manufacturing processes, current MOSFETs generally have common shortcomings in the high total gate charge (Qg) and the high figure of merit (FOM). In addition, the existence of the dimple structure PA131 further makes worse the aforesaid shortcomings.
The aforesaid total gate charge stands for the charge required for the gate to put the MOSFET in a complete conductive state. The total gate charge and the start-up speed of MOSFET are highly related. A high total gate charge would reduce the switching speed, but increase the gate loss; such that the switching loss would be increased, but the efficiency is reduced. In addition, the FOM is determined by the on-state resistance (Rdson) and the total gate charge (Qg); in particular, by the value of Qg×Rdson. A high FOM implies poor performance in the conductive loss and the switching loss.
Hence, while in forming the trench of the MOSFET, the topic of reducing the total gate charge and the FOM by improving the dimple structure is crucial to the art.